Technical Information Pages for the Restoration of the BMW R75 and Zündapp KS 750.

Editor:   ERSATZTEIL- DIENST   Hans-Peter HOMMES       D-41748   VIERSEN   Tiefenstraße 10       Tel. 02162 - 8100933

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The old valve seat rings.   Quite often nobody thinks about the old valve seat rings when restoring an engine. Unfortunately it happened during our trips several times that an old original valve seat ring became loose from the cylinder head. The special thing is that it does not happen during the drive that the valve seat ring falls out.   It mostly happened after a break when we started our engines again and one of them did not want to start. We then recogniszed the missing compression on one cylinder and then it was clear that a ring of the cylinder had become loose and kept the valve open.   The one who thinks he could demount the cylinder head and put the ring back into its original position I have to tell that this is not possible. The ring is larger by almost 1/10 mm than the hole where it has to be put back into. In most cases a tow rope helps and then an other cylinder head.
You may be lucky that no further damages occur. But if you absolutely want to hear the engine again and tow-start the bike, then there can be more damages. So if you find out that ignition and fuel delivery are OK and the spark plugs also look like they should, then check the compression with your thumb. When the compression is missing on one cylinder the reason could be the valve seat ring that has fallen out. When we restore engines and cylinder heads we always put new valve seat rings as a matter of principle.		The ring of the inlet valve has fallen out.

Valve seat ring field report

We decided to start our way back to Oslo with our six Wehrmachtsgespannen in the evening. Somewhere just before Oslo we wanted to camp in our tents and then take the ferry back to Kiel at 01 p.m. In early June days are long in Norway and we expected only 5-6 hours of real night.

Our drive led us through some long tunnels, one of them forcing up like a corkscrew into the barren highland of Hardan­gavidda.

The bikes ran well, as it should be, and as we went back home we all hurried up. The route to Oslo is approx. 350 km. except for a short fuel stop we covered the distance without a break.

After six hours driving around 2 a.m. at night I found a small forest track shortly before Oslo which we took to put up our tents. I stopped my engine and put my tent up as all the others too. Then I wanted to drive my bike to another spot where it was less in the way. The engine started and made an ugly rattle when accelerating.

I knew this noise from somewhere. It sounded very much like fallen out valve seat rings. I knew immediately I would not have a quiet night at this place.

At the same time it started to rain and everybody fled into the tents. For the moment I could not do anything, so sleep was the best thing. We wanted to leave at 10 a.m. and Hans-Gerd should set his alarm clock.

He set his alarm which rang at 7 in the morning already.  We tried to explain to Hans-Gerd that it was far too early but we could not stop ‘the early bird’ from getting up to deal with all sorts of occupations.

I wasted a few thoughts on my KS and slowly dozed off again.

Suddenly I heard the familiar sound of kicking a starter. Then the engine started. Some accelerations and Hans-Gerd shouted: ‘Peter, the valve seat ring has fallen back in again and the engine runs fine.’

I thought that this was great although I had never experienced that a fallen out valve seat ring could get back in again that easily. It would be too good to be true but I liked to believe it.

All the others were awake now and I heard the zippers of tents, the engine noise that I enjoyed. 

And then Udo’s voice shouting putting his head out of his tent: ’Hans-Gerd! This is my bike!

Switch the engine off. Peter’s is the one on the right side.’

Hans-Gerd reckoned shrugging his shoulders ‘these things all look alike’.

Depressed I shut myself away in my sleeping bag and slept for another hour. Then I put my tent together, got my tow rope and hung my KS behind Udo’s Wehrmachtsgespann. He towed me the 20 km to the ferry. To tow a Wehrmachtsgespann with a Zündapp KS750 is no problem even for longer distances.

If a valve seat ring loosens you can not get it back at its place with on vehicle tools. Each engine I repair nowadays gets new valve seat rings. It does not matter how good the existing ones look. On some of my trips it happened a few times that the falling out of a valve seat ring spoiled the continuation of the journey of some of the drivers.

BMW R75 and Zündapp KS 750 drivers alike had this problem frequently.

However it never happened to me with my new valve seat rings.

We offer: Spare parts + Accessories + Repair for Engines, Transmissions, etc. of  Zündapp KS 750 and 600

We offer: Spare parts + Accessories + Repair of BMW R75 and Zündapp

H-P Hommes Ersatzteil-Dienst
Ersatzteile + Instandsetzungen
repairing + restoring